The Hilton Mystic is nice in Connecticut. It's nothing fancy, but it's near the Aquarium, Mystic Seaport, and the Sub Base. Maybe catch a concert at the Casino, and the beaches in Rhode Island are not that far away.

How about Harrisburg, PA. Small city, close to Lancaster and Gettysburg for family jaunts. I live here and lots of great things. Kids that age will LOVE Knoebels park, family atmosphere, no admission

Good choice and easy 3hr drive on I-78 from NYC.
Just did the drive last week.
Another good choice in that area is nearby Homewood Suites Lancaster, PA.
Smack in middle of charming Amish country, and near Dutch Wonderland amusement park and an outlet mall.
Lots of family vacationers in summer.